Project Summary/Abstract Unintended nerve injury is the major cause of morbidity for many surgeries, especially in soft tissue orthopaedic operations. Distinctive visualization of nerves from adjacent connective and fat tissues remains challenging, and therefore is the major reason for the possible incidence of surgical nerve damage. Fluorescence guided surgery (FGS) with nerve-highlighting agents has the potential to improve nerve identification. Existing FGS devices are designed for fluorescent agents in the near-infrared or NIR (700 nm to 900 nm), such as ICG and Methylene blue. However, most of the demonstrated nerve labeling agents are in the visible range. Adapting NIR systems to visible wavelengths is not trivial, mainly because of the presence of the strong white light background in the operation room (OR) that overwhelms the weak fluorescence signal. In this R&D program Physical Sciences Inc. (PSI), in collaboration with Dartmouth College (Dartmouth), proposes to develop a versatile intraoperative fluorescence imager that can capture highly-specific fluorescence images at any wavelength in the visible to NIR range. The key innovation of this technology is the use of spatially modulated illumination to eliminate the negative impact of the ambient light background which is essentially a uniform (in space) continuous wave. A time- gated detection scheme based on a high-speed camera and a low duty cycle (1/100) pulsed light source will be used to enable efficient rejection (~99%) of the ambient light background. In Phase I, we will develop and optimize fiber-connected pulsed laser source and a spatially modulated illumination unit at PSI, and then incorporate them into an existing fluorescence imaging system at Dartmouth. The completed imaging system will be tested on tissue phantoms, ex vivo tissue specimens, and finally in in vivo mice. A large-scale in vivo study will be performed during a subsequent Phase II program. This R&D project will lead to a reliable solution enabling intraoperative fluorescence imaging in both NIR and visible range, while with little/no susceptibility to ambient light interference. This will promote intraoperative fluorescence imaging procedures to be seamlessly integrated into current clinical workflows for optimal patient outcome.